Summary Subjective cognitive decline (SCD), the self-reported perception of memory or cognitive problems, is receiving increasing attention as a risk factor for the development of Alzheimer?s disease (AD). Since SCD manifests before the onset of clinical impairment, it might be the optimal stage/window of time at which to intervene with preventative therapies for AD and age-related dementia before the progressive neurological loss and irreversible cognitive impairment. Recently, mind-body interventions have demonstrated their potential in preventing cognitive decline. Nevertheless, these mind-body therapies encompass a family of complex practices, each with different characteristics and focus. Therefore, they may be associated with different mechanisms and treatment effects. Baduanjin (BDJ) is an innovative and simple mind-body exercise consisting of eight simple movements that can be easily practiced at home with video guidance, thereby making it a more suitable option for older adults with cognitive decline than other more complex exercises. In a previous study, we found that BDJ significantly improved memory and executive function, resting state functional connectivity of the hippocampus and dorsolateral prefrontal cortex, and grey matter volume of the medial temporal area and putamen in older adults. In addition, we found that BDJ could produce significantly greater cognitive function improvement, as measured by the Wechsler Memory Scale (WMS) sub-score, and more extensive grey matter brain volume changes at medial temperal lobe and putamen. A more recent pilot study showed that, compared to walking and health education, six months of BDJ significantly improved cognitive function in patients with MCI. These findings provide a solid foundation for the current application. This proposal aims to investigate 1) the preventative effect of longitudinal BDJ on cognitive decline, 2) the modulation effect of BDJ on resting state functional connectivity of the hippocampus and bilateral dorsolateral prefrontal cortex, and 3) the modulation effect of BDJ on brain morphometry in individuals with SCD as compared to controls. We believe that this study will 1) significantly improve the prevention of MCI and AD and directly benefit patients suffering from these highly prevalent disorders, 2) enhance our understanding of the neurobiology through which mind-body interventions affect cognition and health, and 3) advance our understanding of the pathophysiology and development of SCD, AD, and age-related dementia.